Just stirring the pot...
Despite the overwhelming negativity in this forum, I just wanted to drop a note in here to say that I just completed a relatively pleasant AC itinerary (STL-YYZ-LHR and LHR-YYZ-STL), all traveled in coach. I am *G with US so that certainly helped with the check-in and boarding, not to mention the lounge access. Speaking of which the MLL blows away the US Airways club by far, especially the sad, sad PHX US clubs. Your booze selection is quite appreciated!
I am used to bypassing the general check-in counter queues here in STL when flying US or UA, but it should be noted that the AC "counter" is a sort of step-child of the United counter, which means no *G lane, and usually only one person manning the ship and no kiosks. However, given that there are usually no more than 50 people ever arriving for a AC flight, that line is not likely to be an issue. I do find it amazing that enough people want to go to St Louis, MO from YYZ to justify twice daily service.